Configuration Registers

The global configuration command - config-register is used to modify the behaviour of the router. Weather or not it boots from saved configuration. Weather or not it boots from the flash or the boot-proms.

The following page is an excellent reference for configuration registers http://www.cisco.com/univercd/cc/td/doc/product/access/acs_mod/cis4000/4000m/4000sig/vconfig.htm

In summary these Boot Registers are quite handy:

• The value range is from 0x0 to 0xFFFF.
• 0x2102 is the factory-default configuration register value.
• 0x2142 boots from flash without using NVRAM contents good for password recovery.
• 0x2101 boots from boot prom image not flash, good for upgrading image on flash.
• 0x2141 boots from boot prom and ignores NVRAM contents.
• 0x141, which disables the Break key, ignores the NVRAM configuration, and
  boots the default system image from ROM.